1. Field of the Invention
The present invention relates generally to wire pullers and cords which can be used to pass through pipes or other narrow passages.
2. Description of the Related Art
Wire pullers can be used to draw a long cable or the like through pipes or other narrow passages in a building. In the case of passing through a long narrow passages, e.g. with a length more than 30 meters, the wire pullers need to be provided with sufficient compressive strength and tensile strength to bear the friction from the pipes and other resistances. In addition, the distal ends of the wire pullers also need to remain flexible. Therefore, it is required to provide different physical properties to different segments of the wire pullers. For instance, the segment close to the distal end can be provided with smaller outer diameter to remain flexible, while the segment remote from the distal end can be provided with larger outer diameter to have better structural strength.
For this purpose, the Taiwanese invention patent no. TW 483208 discloses a wire puller and it shows the flexibility of the distal end of the wire puller can be enhanced by varying the pitch of the threads or by varying the elongation of the distal end thereof during the elongation process. Thereby, different segments of the wire puller can have different physical properties.
Nevertheless, it requires higher processing skills to implement the above-mentioned process in extrusion molding treatment of the resin wire pullers. It is so because the processing parameters in a part of the segments of the wire puller are different from those in the other part thereof, and yet these segments need to be extruded continually. As a result, such extrusion molding treatment usually leads to lower yield and higher cost.